The presence of non-expressed intervening sequences of DNA (introns.) in globin genes has led to suggestions that each expressed sequence codes for a domain of specific function within the protein. We plan to explore this possibility by preparing the putative domains by selective cleavage of the hemoglobin chains and characterizing each resultant peptide with reference to the known function of its amino acid residues in the intact molecule. Initial experiments with the intact chains have established improved procedures for the preparation and handling of separated globin chains, their reconstitution to hemoglobin, and their cleavage to peptide fragments.